Human immunodeficiency virus type 1 (HIV-1) infection is initiated by binding of the virus envelope glycoprotein gp120 with the primary cellular receptor CD4. This interaction creates a high affinity binding site (CD4i) on gp120 for the chemokine receptor (CXCR4 or CCR5), designated as coreceptor. CCR5 is a G protein coupled receptor (GPCR) and the principal coreceptor used during natural infection and transmission of HIV-1, including sexual transmission. The binding of the gp120-CD4 complex to CCR5 initiates a series of conformational changes in the envelope glycoprotein and facilitates HIV-1 fusion to the target cells. Therefore, the initial events of the HIV-1 infection process have been a major target for developing new classes of HIV-1 inhibitors, named as entry inhibitors. Several experiments and Phase l/ll clinical trial results indicate that CCR5 is a valid target for discovery of new entry inhibitors. Since there is no three-dimensional structure of CCR5 available, structure-based design is not feasible at this time. Recently, we have identified, from a large set of reported data, important features (pharmacophore models) for CCR5 antagonists. We hypothesize that the pharmacophore based models can be used to effectively and rapidly identify CCR5 antagonists from large drug-like chemical databases. The specific aims to accomplish the objective of identifying such inhibitors are: (1) to identify small molecule organic lead compounds that bind to CCR5 by virtual screening of large databases; (2) to identify lead HIV-1 entry inhibitors that block binding of the gp120-CD4 complex to CCR5 by biochemical and virological screening assays; and (3) To design and synthesize a selected focused library. Overall, this phase of the R21 project will provide new lead compounds that act as potential HIV-1 entry inhibitors. The long term goal is to optimize the lead compounds through chemical syntheses and structure activity relationship (SAR) analyses and select the 3-4 best compounds for further preclinical studies.